Thursday, 25 February 2016

calculus - Trouble with trigonometric limits without derivatives



I am trying to find the following 2 limits as part of a series of 4 exercises following out lectures. We haven't really learned derivatives yet, so I can't just slap L'Hospital and be done with it.



The first two I could solve with Taylor Expansions, but I still need to solve:



limx0exsinx1x2


Taylor Expansion of sin didn't work here, and I don't know how to deal with the ex.



limx0xsinxcosx1



Given sin2x=cos2x1 I tried multiplying by cosx+1cosx+1, which lead me to xcosx xsinx and then I don't know what else to do. (SOLVED) I suppose I could simplify this to xcotxxsinx, which leads to -2.


Answer



You have



ex=1+x+x22(1+ϵ1(x))



and



sin(x)=x+x2ϵ2(x)




cause xsin(x) is odd.



then the limit is 12


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